Github user dawidwys commented on a diff in the pull request:
https://github.com/apache/flink/pull/3624#discussion_r108364477
--- Diff: docs/dev/libs/cep.md ---
@@ -124,13 +124,70 @@ val start : Pattern[Event, _] = Pattern.begin("start")
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-Each state must have an unique name to identify the matched events later
on.
+Each state must have a unique name to identify the matched events later on.
Additionally, we can specify a filter condition for the event to be
accepted as the start event via the `where` method.
+These filtering conditions can be either an `IterativeCondition` or a
`SimpleCondition`.
+
+**Iterative Conditions:** This type of conditions can iterate over the
previously accepted elements in the pattern and
+decide to accept a new element or not, based on some statistic over those
elements.
+
+Below is the code for an iterative condition that accepts elements whose
name start with "foo" and for which, the sum
+of the prices of the previously accepted elements for a state named
"middle", plus the price of the current event, do
+not exceed the value of 5.0. Iterative condition can be very powerful,
especially in combination with quantifiers, e.g.
+`oneToMany` or `zeroToMany`.
+
+<div class="codetabs" markdown="1">
+<div data-lang="java" markdown="1">
+{% highlight java %}
+start.where(new IterativeCondition<SubEvent>() {
+ @Override
+ public boolean filter(SubEvent value, Context<SubEvent> ctx) throws
Exception {
+ if (!value.getName().startsWith("foo")) {
+ return false;
+ }
+
+ double sum = 0.0;
+ for (Event event : ctx.getEventsForPattern("middle")) {
+ sum += event.getPrice();
+ }
+ sum += value.getPrice();
+ return Double.compare(sum, 5.0) < 0;
+ }
+});
+{% endhighlight %}
+</div>
+
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+start.where(
--- End diff --
It is not that obvious but the `lazy` keyword plays the role of avoiding
calling `getEventsForPattern`. But I agree the java-ish way is more
straightforward.
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